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The Planets this Month - June 2015

Mercury

Mercury passed inferior conjunction on May 30th and was therefore positioned too close to the Sun to be observable. However, it moves rapidly out from the Sun so that two weeks later it becomes visible as a morning object for observers in the tropics and Southern Hemisphere. The planet subsequently climbs higher in the sky and brightens each day until it reaches a peak altitude on June 24th, the date of greatest elongation west (22.5 degrees from the Sun). Also on this day Mercury passes 2 degrees north of orange giant star Aldebaran (α Tau) the brightest star in the constellation of Taurus "the Bull". At magnitude +0.4 Mercury is half a magnitude brighter than the star with the pairing making a lovely early morning binocular / small telescope view.

It should also be noted that once past greatest elongation west, Mercury continues to brighten as it begins to draw into the Sun. For example, the planet shines at mag. +1.7 on June 15 but by month's end it has brightened to magnitude -0.1. From northern temperate latitudes, Mercury is a more difficult catch as it battles against the long morning twilight. The best time to try and catch it is for a few days on and around June 24th when it should be visible low down above the east-northeast horizon just before sunrise. A pair of binoculars will easily show the magnitude +0.4 planet although be careful not to confuse it with nearby Aldebaran.

The diagram below shows the June / July morning apparition of Mercury from a latitude of 35S (approx. equal to Sydney, Cape Town and Santiago).

Venus

The brightest object in western sky after sunset is Venus with the planet remaining well placed for observation throughout the month. On June 6th it reaches greatest elongation and on this day is positioned 45 degrees east of the Sun.

Currently moving eastward the declination of Venus decreases by 10 degrees as it moves from Gemini into Cancer and then into Leo. Consequently, the planets period of visibility decreases from 3.5 hours to less than 2 hours for observers located at Northern Hemisphere latitudes. For those living in the Southern Hemisphere the period of visibility remains around the 3-hour mark for the complete month.

There are three superb Venus conjunctions visible during June. On June 12th and 13th the planet slides less than a degree north of splendid open star cluster M44 "The Beehive", making a wonderful binocular sight. Then on June 20th, the waxing crescent Moon passes 6 degrees south of the planet. Finally Venus closes the gap on Jupiter and on the last day of June the two planets will be less than half a degree apart. To the naked eye they will appear stunning. Through binoculars and a telescope at low power both planets will appear in the same field of view, although Venus is about 10x the brighter of the pair.

The magnitude of Venus increases slightly from -4.3 to -4.4 with its phase decreasing from 53% to 34% during June.

Mars

Mars reaches solar conjunction on June 14th and therefore is unobservable throughout the month.

Jupiter

Jupiter remains an early evening object throughout June although it's now long past opposition and heading towards solar conjunction. The largest planet of the Solar System is visible towards the west as soon as it gets dark, but sets before midnight by months end. It's brightness decreases slightly from magnitude -1.9 to -1.8 as the month progresses.

The giant planet continues on a direct motion path, starting the month in Cancer before passing into Leo on June 10th. At the start of June, brighter Venus (mag. -4.3) is located about 20 degrees from Jupiter. It then closes the gap each subsequent evening before catching Jupiter at the tail end of the month. On June 30th, the two planets will be less than half a degree apart.

On June 21st, the waxing crescent Moon passes 5 degrees south of Jupiter.

Saturn

This month Venus and Jupiter dominate the early evening sky with Mercury visible for a time in the morning sky but the night belongs to Saturn. The planet is only just past opposition (May 23rd) and remains superbly placed for observation during June. It's currently moving retrograde in western Libra and visible towards the southeast (NH) / east (SH) as darkness falls. Saturn can be observed practically all night and is better seen from southern latitudes where it's situated much higher in the sky.

Since now past opposition the apparent brightness and apparent size of Saturn will gradually decrease as the Earth moves away. During June, its magnitude decreases from 0.0 to +0.2 with the apparent diameter shrinking slightly from 18.5 to 18.0 arc seconds.

Saturn's wonder of course is its ring system. They are currently tilted at 24 degrees from our perspective and even a small 80mm (3.1-inch) telescope will easily show them. At magnification 100x the rings are nicely visible, tightly circling the central gem of Saturn. Increase the magnification to 200x or greater (seeing permitting) and the ring shadow on the planet, the darker outer A ring, the lighter B ring, subtle shadings and colour changes on Saturn's surface may be detected.

A good quality larger telescope, with its increased light gathering capability and higher magnification capability will of course show greater detail. For example, a 200mm (8-inch) scope can under good seeing be used to up to 400x magnification and will also reveal the 0.7 arc seconds wide Cassini division, the Enke division, the hazy C-ring as well as up to half a dozen of Saturn's satellites.

The almost full Moon passes 2 degrees north of Saturn on June 1st and again on June 29th.

Uranus starts the month as a morning object in Pisces with the planets visibility steadily improving as the month progresses. For Northern Hemisphere based observers at the start of June, it's visible above the eastern horizon for about an hour before twilight interferes. By months end the planet is much higher in the sky, rising more than 4 hours before the Sun.

Observers located further south have it even better with Uranus well placed in the morning sky throughout the month. At the beginning of the June the planet rises some 4 hours before the Sun and by the end of the month it's visible before midnight.

Uranus is a distant ice giant that shines at magnitude +5.9 and therefore bright enough to be seen with the naked eye from a dark site. Unfortunately most people don't have the luxury of such fine seeing conditions and therefore a pair of binoculars or small telescope is usually required to spot the planet.

On June 11th, the waning crescent Moon passes 0.5 degrees south of Uranus and an occultation is visible from South and East Australia, New Zealand, Fiji and Samoa (20:26 UT).

Neptune shines at mag. +7.9 and is now well placed for observation amongst the stars of Aquarius. By months end the most distant planet of all rises around midnight from northern temperate latitudes and much earlier for those located further south. It's currently located about 30 degrees southwest of the Great Square of Pegasus and a few degrees southwest of star lambda (λ) Aqr (mag. +3.7).

On June 9th, the last quarter Moon passes 3 degrees north of Neptune. Three days late Neptune reaches its first stationary point, signaling the beginning of this year's opposition period. The planet then commences retrograde motion.